How to render All layers in my Compositor at once
You selected Only render the active layer option in the Render layers list. 



With this option only currently selected render layer (active one) will be rendered while others won't be; thus while compositing you'll see new results only on this active render layer.
From manual:


  Using Render Layers can save you from having to re-render your entire image each time you change something, allowing you to instead re-render only the layer(s) that you need.


Deactivate this option and all the Render layers will be rendered again when you press F12 (or with any other way).